1. Field of the Invention
The present invention generally relates to digital radio frequency (RF) links, and more particularly to a radio frequency link performance tool (RFLPT) process and system, which predicts the successful transmission of digital packets over an RF link with RF interference, such as jamming or Electronic Warfare (EW) effects, and without an intentional interference (non-jamming) environment.
2. Related Art
A method for optimizing an RF communications network for use in a battlefield environment is described in U.S. Pat. No. 6,232,909 issued to Masciulli, the complete disclosure of which is herein incorporated by reference (hereinafter referred to as “the '909 patent”). The '909 patent describes a process for determining the performance of radio frequency links in the United States Army's Enhanced Position Location Reporting System (EPLRS) with a high level of statistical confidence. The method described therein includes determining a statistical difference between a mean propagation loss for an EPLRS RF link based on measured RF propagation loss and Terrain-Integrated Rough-Earth Model (TIREM) calculated RF propagation loss, establishing a margin of error based on the statistical difference to arrive at a confidence level of the RF propagation loss, determining a computed signal to noise ratio (S/N) based on the confidence level, for the benign and jamming case, and determining a Probability of Communication (PCOM) value based on the computed S/N value.
EPLRS is an integrated communications system that provides near real-time data communications, such as global positioning communications including position/location, navigation, identification, and reporting information on the modern battlefield. The system, which may include 300-1500 terminals in a division with up to five Network Control Stations (NCS), utilizes spread spectrum technology and frequency hopping error detection and correction and is capable of supporting multiple communication channel operations. Understanding RF link performance is critical to the effective use of EPLRS. RF link performance is broadly characterized by the ratio of desired EPLRS received signal to noise within the communication channel (the S/N ratio).
Conventional systems and methods utilizing the EPLRS capacity model simulations use various parameters to characterize the desired signals, propagation characteristics, communication, and battlefield scenarios. While the signal models work quite well under a number of scenarios, the nature of the problem is such that the models are unable to account for many situations that can and do occur on the battlefield. As such, the method described in the '909 patent uses statistical methods to account for the variability associated with certain parameters used to compute the EPLRS RF link performance. In the case of a communications system such as EPLRS, the RF noise background and RF propagation loss are two parameters that are difficult to model with great accuracy. Thus, statistical methods can provide a quantitative level of confidence, based on measured data and certain numerical assumptions.
According to the method taught in the '909 patent, the key parameter used to measure a single EPLRS RF link performance is the PCOM which is a function of S/N. PCOM is the probability of a single EPLRS pulse being successfully received over a single link in one direction. The EPLRS system employs four modes of operation, which provide various levels of anti-jamming capability. These algorithms provide a PCOM for each EPLRS RF link based on the mode of operation and random Gaussian (white) noise in the RF noise environment.
The EPLRS PCOM analysis tool can provide a user with a quantitative level of confidence for predicting EPLRS RF link performance. Currently, the U.S. Army uses a model called the Terrain-integrated Rough-Earth Model (TIREM) to calculate a mean RF propagation loss value given a terrain profile along the RF link path. For general background, see DOD Electromagnetic Compatibility Analysis Center (ECAC) document ECAC-HDBK-93-076, entitled “TIREM/SEM Handbook” dated March, 1994, chapter 5 “Model Limitations,” page 5-5, the complete disclosure of which is herein incorporated by reference. According to the TIREM/SEM Handbook, TIREM's mean calculated RF propagation loss is −0.6 dB with a standard deviation of 10.5 dB. However, TIREM is static and does not adequately account for changes in RF signal and noise conditions, resulting in the miscalculation of RF link propagation losses.
While one could attempt to refine the model in order to account for various propagation conditions, the possible combinations are simply too numerous. Rather than attempting to improve the model, the process described in the '909 patent performs a statistical analysis of all the model parameters required to calculate the EPLRS S/N ratio, then identifies the parameters that have the most inaccuracies, making those parameters the limiting factor during subsequent calculations. For example, the method in the '909 patent accounts for the inaccuracy contained in the TIREM mean value, by using a process that provides a margin based on random variables and the normal distribution function. This margin provides a stressing factor to the mean calculation of S/N, which allows for a higher confidence that the model will represent the real world by a certain percentage of time.
Another example is the RF noise background used for the noise calculation, which is separate from the broadband jamming noise. Reference is made to ITT textbook entitled “Reference Data For Radio Engineers” fifth edition (October, 1968) page 27-2 FIG. 1 “Median Values of Average Noise Power from Various Sources,” the complete disclosure of which is herein incorporated by reference. These values are assumed values that can be used as stress factors when calculating the N in the S/N ratio.
Although the '909 patent provides the U.S. Army's EPLRS as the RF link, there is a need to include all digital packet structures transmitted over RF links. Moreover, the conventional models use TIREM to calculate a mean RF propagation loss value given a terrain profile along the RF link path. However, the S/N value calculated from the TIREM's nominal propagation loss value does not account for the standard deviation associated with the TIREM calculated propagation loss and actual measured values of propagation loss. Therefore, there remains a need for improvements to the conventional techniques.